Plastic from old milk jugs at left. A DremelFuge -- a homemade centrifuge for use with a rotating tool like a Dremel -- made from plastic from old milk jugs at right. Michigan Tech photo.

HOUGHTON (WWJ) — What do you do with old plastic milk jugs?

Sure, you can recycle them conventionally in a municipal collection program. But now, a professor at Michigan Technological University says you can save a lot more energy and money by turning them into plastic filament — the raw material of a 3D printer — and making your own plastic goods at home.

The study, led by Michigan Tech’s Joshua Pearce, found that making your own plastic 3D printer filament from milk jugs uses less energy — often a lot less — than recycling milk jugs conventionally.

Pearce’s team did a life-cycle analysis on a run-of-the-mill milk jug made from HDPE plastic. After cleaning it and cutting it in pieces, they ran it through an office shredder and a RecycleBot, which turns waste plastic into 3D printer filament.

Compared to an ideal urban recycling program, which collects and processes plastic locally, turning milk jugs into filament at home uses about 3 percent less energy.

“Where it really shows substantial savings is in smaller towns like Houghton, where you have to transport the plastic to be collected, then again to be recycled, and a third time to be made into products,” said Pearce. In those cases, the energy savings skyrocket to 70 to 80 percent. And recycling your own milk jugs uses 90 percent less energy than making virgin plastic from petroleum.

Pearce, an associate professor of materials science and engineering, as well as electrical and computer engineering, compared the cost of making your own filament with buying it. He said filament retails for $36 to $50 a kilogram (2.2 pounds). But you can produce your own filament for 10 cents a kilogram if you use recycled plastic.

“There’s a clear incentive, even if you factor in the cost of buying the RecycleBot,” Pearce said.

Commercial versions of the RecycleBot like the Filastruder cost under $300.

HDPE plastic isn’t ideal for making household goods, Pearce said, because “it shrinks slightly as it cools, so you have to take that into account. But if you are making something like a statue or a pencil holder, it doesn’t matter.”

This new recycling technology has caught the eye of the Ethical Filament Foundation, which aims to improve the lives of waste pickers, who scour other people’s trash for items to sell or recycle.

“In the developing world, it’s hard to get filament, and if these recyclers could make it and sell it for, say, $15 a kilogram, they’d make enough money to pull themselves out of poverty while doing the world a lot of good,” Pearce said.

The study, “Life-Cycle Analysis of Distributed Recycling of Post-consumer High Density Polyethylene for 3-D Printing Filament,” by Megan Kreiger, Meredith Mulder, Alexandra Glover and Pearce, all of Michigan Tech, was published Feb. 12 in the Journal of Cleaner Production. An open access version is available from Academia.edu.